My 98 k2500 with vortec 7.4 will start, and run normal, for about 1 to 2 seconds, and then will not keep running. I have used my obd 2 code reader, and it comes up no codes present. Anyone ever have this problem, or hear about it? Please help!

it sounds like the security system is shutting off your fuel injectors because it is not seeing the correct information from the ignition. Is the security light coming on? If it comes on for 5 seconds and then goes out, the system is okay. If the light stays on, you need to diagnose the passlock system for a failure somewhere.

No, the security light goes out almost immediately, but sometimes it blinks a few times and then goes out. It never actually stays on for any length of time longer than 5 seconds. I was wondering if it could possibly be a fuel pump relay? I can hear the pump running, even after it dies tho. And I thought maybe it was out of gas so I put in another 3 gallons fresh from the gas station via gas can, and I made sure it was clean and dry before putting gas in it to bring to the truck(I've had water in a gas can before cause problems, and one time a friend used my gas can for diesel and I had to rebuild the carb on my Harley because of it, so now I am pretty careful with my fuel contamination problems

Also, the scan tool I use is an INNOVA 3100a CanOBD2 code reader. And I just fried my starter trying to get it going lol. My luck this year! Any input is welcome, I will have another starter hopefully by the middle of the week

the passlock system shuts off the injector pulse signal at the computer. everything else works normally. that's why it runs for a few seconds and then shuts down. If you manually supply the fuel you can keep it running and check to see if you have injector pulse.

Ok, I haven't gotten a new starter on it yet, so I haven't checked for injector pulse, but for argument's sake, let's pretend there was no injector pulse due to the passlock system shutting it down...what would be the remedy

CrazyW wrote:> Ok, I haven't gotten a new starter on it yet, so I haven't checked for> injector pulse, but for argument's sake, let's pretend there was no> injector pulse due to the passlock shutting it down...what would be> the remedy

if it is the passlock that is turning off the injector pulse then it could be that it has lost the memory of what the key code was. You just do a key relearn and see if it works again. If that doesn't do it you may have a bad passlock circuit.

there should be three wires that go the the lock cylinder for the passlock sensor. Red and white, 12V from the passlock module with a 10 ohms resistor. orange and black, sensor return to the passlock module. and Yellow, passlock signal. A tech2 scanner can see if there are codes in the passlock module and you can look at the voltage for the passlock signal. You can use the tech2 to tell the passlock module to learn the key.

Or you can manually check the voltage on the yellow wire. It should be 5 volts when you start. When you turn the key the voltage should drop. if you don't have the five volts or you have 5 volts but it doesn't drop when you turn the key you may need a new lock cylinder or the VCM may be bad.